[SignalOne] 8072's

[EDWARD SCHUMACHER]

Per the early info from the newsletters, the 8072 will torque regardless. May only apply to tubes produced before this was discovered but don't know for sure. RCA was notified but don't have any documentation showing they ever did anything about it. I have brought on a failure from not regreasing the heat sink system completely with a good rebuilt tube installed. The fuse blew and saved the rest of the power supply but not before overheating both the screen and grid resistors. They were harder to find than some of the other parts I have needed. Good cooling seems to alleviate the problem but can't say for sure. I am still running an original final with only slightly lower output with no signs of shorting. Heat seems to be the enemy and the tips on better cooling seem to help.

On another tack re Variacs, my experience here is that you must check your source from Edison. Last winter I found 133, yes that is 133VAC at my outlets. This puts older rigs relying on line voltage to run very high especially on PA plates! This is where the variac or a bucking transformer is invaluable if this condition is constant. Modern rigs running thru regulated power supplies never see this problem. Many older rigs were pre 125 and up sources.


Ed, WA9GQK